In typical fuel tanks, the filling-fixture, that is, the highest part of the intake tube and that particular part which carries the tank closure, is closed by various connection devices placed thereon. Conventional connection variants include, for example, hose clamps, pinch-rings, or the like. Sealing between the connection of the intake tube, the filling support and the tank closure, as a rule, is effected by one or more O-rings.
Future lawfully imposed permeation rates, where the intake tube is concerned, cannot be fulfilled by the above described, conventional filling-fixtures. The permeation rate for a single filling-fixture, which is affixed to the intake tube by one of the above connections with O-rings, lies at approximately 5 mg/24 h solely for sealing the connection. Estimated limiting values for a complete filling-fixture, including an automatic tank closure show allowable maximum values of permeation rates of 10 mg/24 h for Low Emission Vehicles, Stage 2 (LEV-II) and 5 mg/24 hr for Partially Zero Emission Vehicles (PZEV). The connection of the filling-fixture to the intake tube, to fulfill PZEV demands would lead to a situation where no additional permeation could possible occur in the tank system. At the present time, this is not technically possible to achieve.